The present invention relates to an electronic control arrangement wherein existing electronic motor control circuitry of a motorized assembly may be used to control one or more auxiliary devices.
It is common practice to control the operation of a pair of electric motors, used to drive respective wheels of a motorized wheel-chair assembly, by varying the pulse width of a modulated signal applied to each motor.
Each motor is typically connected across a transistor bridge circuit, the transistors of which may be selectively switched to vary the direction in which the motor is rotated.
It is also common practice to provide such motorized wheel-chairs with further motors or other actuators, the operation of these devices being controlled by further electronic control circuitry, independent of that of the two main drive motors.
It is an object of the present invention to reduce the overall amount of electronic control circuitry required to control the operation of two main drive motors and at least one additional motor or other actuator of a motorized assembly.
In accordance with the present invention, there is provided a motorized assembly comprising:
first and second bridge circuits, the two arms of each bridge circuit each comprising a first and a second electronic switch connected in series;
a respective drive motor connected between the two arms of each bridge circuit, at points intermediate the electronic switches of each of the two arms;
an auxiliary motor or actuator connected between one arm of the first bridge circuit and one arm of the second bridge circuit, at points intermediate the electronic switches of each of the two arms and in series with at least one electronic switch; and
electronic control means arranged to operate the electronic switches to selectively control the operation of the drive motors and the auxiliary motor or actuator.
A third bridge circuit is thus effectively formed by said one arm of each of the first and second bridge circuits, the switch connected in series with the auxiliary motor or actuator serving as a means by which to electrically isolate the auxiliary motor or actuator, when one or both of the drive motors is/are being operated.
It will be appreciated that such an arrangement obviates the requirement for independent control circuitry for controlling the operation of the auxiliary motor or actuator, resulting in a reduction in the overall cost of the motorized assembly.
Preferably the motorized assembly comprises a motorized wheel-chair assembly, respective traction wheels of which are driven by the drive motors.
Preferably each electronic switch of the first and second bridge circuits comprises a transistor, which is preferably a Field Effect Transistor (FET) and is most preferably a Metal Oxide Semiconductor Field Effect Transistor (MOSFET).
Preferably the electronic switch connected in series with the auxiliary motor or actuator comprises a transistor, which is preferably a Field Effect Transistor (FET) and is most preferably a Metal Oxide Semiconductor Field Effect Transistor (MOSFET).
The auxiliary motor or actuator is preferably connected in series with and between two FET transistors. Preferably electronic control means of the assembly are arranged to operate the auxiliary motor or actuator by applying a control signal to the gates of each of the two FET transistors associated therewith and then switching the transistors of the first and second bridge circuits to apply a pulse-width modulated signal to one or other side of the auxiliary motor or actuator and to connect the opposite side of the auxiliary motor or actuator to ground.
A bootstrap capacitor is preferably connected between the source and gate of each of the transistors connected in series with the auxiliary motor or actuator, to ensure that the transistor via which the pulse-width modulated signal is applied will remain in a conducting state whilst the pulse-width modulated signal continues to be applied.
A resistor is preferably also connected between the source and gate of each of the transistors connected in series with the auxiliary motor or actuator, to provide a discharge path for its parallel capacitance, when a control signal ceases to be applied to the gate of the transistor, to arrest conduction between the drain and source of the transistor.
Also in accordance with the present invention, there is provided an electronic control arrangement for a motorized assembly and comprising:
first and second bridge circuits, the two arms of each bridge circuit each comprising a first and a second electronic switch connected in series;
a further electronic switch arranged to be connected in series with a motor or actuator between one arm of the first bridge circuit and one arm of the second bridge circuit, at points intermediate the electronic switches of each of the two arms; and
electronic control means arranged to selectively operate the electronic switches.
The control arrangement may thus be used to selectively control the operation of respective drive motors, connected between the two arms of each bridge circuit, and of an auxiliary motor or actuator, connected in series with the further switch, between said one arm of the first and second bridge circuits.
Further in accordance with the present invention, there is provided a switching arrangement for connecting a motor or actuator to a pulse-width modulated supply, and comprising:
a Field Effect Transistor (FET) arranged to be connected in series with the motor or actuator; and
a capacitor connected between the gate and source of the transistor, the capacitor forming a bootstrapped gate supply for maintaining conduction between the drain and source of the transistor whilst the pulse-width modulated supply is applied to the motor or actuator thereby.
Preferably the transistor comprises one of a pair of Field Effect Transistors (FETs), between and in series with which a motor or actuator may be connected, each transistor having a respective bootstrap capacitor connected between its gate and source for maintaining conduction of that transistor whilst a pulse-width modulated supply is applied to the motor or actuator thereby.